The present invention relates to a method of deriving a (surrogate) measure of stiffness and/or strength of sections of the stem of a felled tree (e.g., so as to be determinative of possible destinies of logs to be cut from the stem), a method of log making or log use determination for logs made or to be made from a felled tree with a view to maximizing stiffness and/or strength related extracted value therefrom, procedures involved in such methods and to related apparatus and means.
The invention also relates to the apparatus useful in such a procedure and to its use.
The timber industry faces a need to efficiently utilise its rather variable forest resource. Timber classification, for example machine stress grading, is currently done at the end of the production chain. This process results in wastage from processing which ultimately proves to have been inappropriate. Clearly, it would be more efficient to measure log properties early in the chain and process the logs accordingly.
As recognised in British Patent 1244699 of Washington State University Research Foundation (the full content of which is hereby included by way of reference) non-destructive individual valuation of wood products is often desirable because of the inherent variability of wood as a material particularly where a wooden member is to be used for a purpose that requires knowledge of its ability to perform to a minimum structural standard.
The aforementioned patent contemplates, in addition to visual inspection, a non-destructive method of grading logs by a procedure where properties are determined along a selected length of a specimen by means of longitudinal energy wave propagation through the selected length thereof. This was achieved by locating a first sensor in proximity to a surface of the specimen at one end of the selected length thereof and locating a second sensor in proximity to a surface of the specimen at the remaining end of the selected length thereof, impacting one end of the specimen itself to set up an energy wave within the specimen to travel in a longitudinal direction to encounter and then move along the selected length of the specimen between the sensors measuring the time of passage of the energy wave between the sensors and determining mechanical properties of the specimen as related to the measured time of passage of the energy wave through the selected length.
A dynamic modulus of elasticity (hereinafter MOE) was derived by the product of (a) the square of the velocity of wave propagation (i.e., length of the selected specimen length divided by the time of passage of wave)(i.e., V2) and (b) the specimen density(xcfx81).
Such procedures disclosed in British Patent 1244699 are not of a kind usable in a forest with a minimum of labour in the time frame usually required for marking up a felled tree which is to then be broken into logs by appropriately positioned cuts.
It is of course possible to assign different destinies to different logs to be cut from the same stem of a felled tree which will maximize the extracted value of the harvesting of the particular tree. This has been recognised in New Zealand and elsewhere by software packages such as those of the New Zealand Forest Research Institute (i.e., the AVIS(trademark) Software) or previously used by LIRO (i.e., the New Zealand Logging Industry Research Organisation).
A device of favour in the log forming industry in New Zealand is of a kind typified by that disclosed in U.S. Pat. No. 5,457,635 of Interpine Export (NZ) Limited (the full content of which is hereby included by way of reference).
U.S. Pat. No. 5,457,635 discloses apparatus for determining cut positions in stems of felled trees. The apparatus has distance measuring means which provide an output signal representative of length for determining lengths along the stem. The apparatus also has diameter measuring means which provides an output signal representative of diameter for determining the diameter of a stem at selected positions along the stem. Data entry means are adapted to receive and output selected information relating to the quality of a stem at various positions along the stem. Computing means are also provided on the apparatus which (in response to input signals from the distance measuring means, diameter measuring means and data entry means) determines the preferred cutting positions on the stem to optimize the millable timber obtained from the stem. Output means allow information determined by the computer means to be presented to the user so that the stem may then be appropriately marked with cut positions.
Such a product however does not provide an indication of a preferred destiny for individual logs to be cut from the stem reliant in any way upon any actual or surrogate measure of stiffness and/or strength. Stiffness and/or strength (whether MOE or a surrogate measure thereof) is a characteristic of the structural quality of the wood in the logs and is fundamental to its performance in certain uses.
The computer software referred to in U.S. Pat. No. 5,457,635 consists of an optimizing algorithm which works in conjunction with a log type file or library. The log type file or library contains specifications for each log type to be considered along with a relative value representing the desirability of each log type. This software is presented with the input of measurements of length, diameter and curvature of the stem. There is also provision for the manual inputting of the number and size of knots (as a quality code).
The input information then allows the algorithm to xe2x80x9cfitxe2x80x9d the best value combination of logs to be cut from the stem thus providing an optimum solution in terms of the value returned by the stem when cut into logs.
The present invention recognises that the MOE is a good indicator of the structural characteristics of timber. The MOE is related to the speed V of a longitudinal compression wave by the relation
MOE=xcfx81V2 
where xcfx81 is the density of the wooden material. In dried wood (about 12% moisture content) it is known that the modulus correlates approximately with the density xcfx81. In a freshly cut stem or log, the density in large measure is due to the free water content, and the value is in the vicinity of 1000 kg/m3. The modulus is determined by the indicator V2 by measurement (preferably at low frequency as hereinafter described) of the velocity V. Indeed the present invention recognises the value of a measure of V or a function of V owing to its 2nd order use in the MOE formula above.
Apparatus such as the PILODYN(trademark) (density penetrometer which estimates only outer wood density) procedure as a measure of wood characteristics is therefore far less attractive as an indicator of wood performance for structural or other purposes than is the longitudinal wave propagation V or function of V (e.g., elapsed time values) procedure hereinafter described to interpolate to logs along the stem length a surrogate stiffness and/or strength (and thus stiffness and/or strength related value enhancing destiny).
The present invention also recognises the value of the simple relationship where V can be determined by determining (particularly at low frequency) an equivalent fundamental resonance frequency (f0) using the relationship
Vxc3x97resonant frequencyxc3x97twice the length (L) of the stem. 
The present invention therefore in a first aspect consists in a method of log making (or at least cut positioning for log making) from the stem of a felled tree with a view to maximizing stiffness and/or strength related extracted value therefrom, which method includes
inducing from an end of the stem of the felled tree a sonic wave (as hereinafter described) to travel along the length of the stem of the felled tree, reflecting repeatedly at the free ends,
deriving by reference to the tree stem length (or multiples thereof) and the appropriate resonant frequency for the stem V or V2 or a function of V or V2,
and then using that output of V or V2 or a function of V or V2 
(i) as a factor in determining cut positions for a number of logs from the tested felled tree stem, and
(ii) as a prime factor in determining end use for each or at least some of the logs.
Preferably for the purpose of steps (i) and/or (ii) there is reference to a library of known stiffness and/or strength characteristics [whether MOE, V2, V, elapsed time, resonant frequency or some other surrogate value] in relation to known sonic wave travel values typical or generic of trees of the felled tree condition.
Preferably the deriving of the function of V or V2 value comprises the steps of at one end of the stem of a felled tree (preferably after the removal of all branches), inducing an energy input (e.g., by striking or otherwise) and
detecting at that same end the resonant frequencies using spectral analysis of the sequence of multiply reflected returns of the input energy and deriving from the spectrum by appropriate calculations a value of V or a function of V by reference to the known length of the stem.
For the purpose of such detection any suitable apparatus may be used by way of example see U.S. Pat. No. 5,396,799 of Ross et al. U.S. Pat. No. 5,396,799 deals with the measurement of an induced acoustic wave past a detector between the ends of a ground supported vertical pole.
U.S. Pat. No. 5,396,799 discloses the use of impacting means to induce the sonic or acoustic wave and a detection of the passage of the wave past a laterally positioned piezo electric transducer based detector. Those or alternative forms of detection and/or wave propagation can be utilised by the present invention.
The present invention however envisages detection at the same end from which the impact is induced so as to minimise the complexity of the process. The function of V then becomes a manual or automatic input to computing means as will hereinafter be described. Such computing means may, for example, be a derivative of the form of apparatus described in the aforementioned U.S. Pat. No. 5,457,635.
The present invention in a further aspect consists in a method of determining a value indicative of stiffness and/or strength or useful for that purpose (e.g., V or a function of V) [which may optionally be squared to provide a better surrogate value of stiffness and/or strength] which comprises
inducing into one end of the stem of a felled tree an acoustical input (e.g., by striking or other means) and
by detecting subsequent reflected sound therefrom or otherwise using that input to provide a measure of resonant frequencies and
by reference to the length of the stem, determining a value indicative of V or V2 or a function or V or V2 (e.g.; MOE) by reliance on the resonant frequencies.
In still a further aspect the present invention consists in a method of log making or log use determination for logs made or to be made from a felled tree with a view to maximizing stiffness and/or strength related extracted value therefrom, said method comprising
(i) determining
(a) at least one or more of
stem diameter,
stern sweep,
branch size,
internodal length,
stern length, and
feasible log length,
(b) a surrogate measure of stiffness and/or strength for the stem derived from the resonant frequency of an induced sound wave along at least the full stem
(ii) by computer or machine reference to a library of known stiffness and/or strength characteristics in relation to known values of the same type surrogate measure of stiffness and/or strength (or a squaring thereof) typical or generic of trees of the felled tree condition and determining value attributed to different stiffness and/or strength characteristics and/or deriving potential cut positions for discrete logs which take account of stiffness and/or strength related values, such cutting positions determining a preferred destiny or range of destinies.
The log making optimisations may be those disclosed in Interpine Export (NZ) Limited U.S. Pat. No. 5,457,635, the full content of which is here introduced by way of reference.
As used herein all reference to the term xe2x80x9csonic wavexe2x80x9d is to be considered synonymous with any energy wave of a vibrational kind that may be induced along the length of the stem of a tree (which might variously be referred to as an induced stress wave, an induced energy wave, an induced acoustic wave, etc).
As used herein reference to deriving or determining a value includes any algorithm into which values are entered and from which V, V2 or a function of V or V2 can be derived whether the actual calculation need be made (e.g., a computer) prior to being used as a surrogate stiffness and/or strength value.
In a further aspect the present invention consists in a method of providing an indicator of or from which stiffness and/or strength can be estimated, which method involves an operative use of apparatus as hereinafter described or as disclosed in our New Zealand Patent Specification No. 337015 filed Jul. 30, 1999.
In still a further aspect the present invention consists in a method of providing an indicator of or from which stiffness and/or strength can be estimated for a felled log of known or measurable length L, said method comprising or including the steps of
striking an end of the felled log whilst having sensing means in contact with the log end to detect one or both of (i) the impulse and at least one echo of the impulse resulting from the striking of that same log end and (ii) multiple echoes of the impulse resulting from the striking of that same log end,
processing the output of at least said sensing means in processing means to derive, using an echo or echoes sensed by said sensing means, a said indicator, and
displaying said indicator or any derivative thereof received from said processing means,
optionally thereafter appropriately marking or otherwise indicating the fate of the log on the basis of the displayed indicator,
said process being further characterised in that said processing means tests frequency transformed data derived from time based echo data with a view to deriving a measure or good estimate of fundamental frequency f0, L has been, is or can be entered into said processing means, and said processing means derives said indicator by reference to both f0 and L.
Preferably said indicator is an estimation of MOE for a green felled log on the basis of an estimation of xcfx81=1000 kg/m3.